Method of patterning a substrate using a sidewall spacer etch mask

ABSTRACT

A method for patterning a substrate in which a patterned photoresist structure can be formed on the substrate, the patterned photoresist structure having a sidewall. A conformal layer of spacer material can be deposited on the sidewall. The patterned photoresist structure can then be removed from the substrate, leaving behind the spacer material. Then, the substrate can be directionally etched using the sidewall spacer as an etch mask to form the substrate having a target critical dimension.

CROSS REFERENCE TO CO-PENDING APPLICATION

This application is a divisional of U.S. patent application Ser. No.17/032,980, filed Sep. 25, 2020, which claims the benefit of priorityfrom U.S. Provisional Patent Application No. 62/905,604, filed Sep. 252019, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

Embodiments described herein relate generally to patterning a substrate.

BACKGROUND

In the manufacture of a semiconductor device (especially on themicroscopic scale), various fabrication processes are executed such asfilm-forming depositions, etch mask creation, patterning, materialetching and removal, and doping treatments. These processes areperformed repeatedly to form desired semiconductor device elements on asubstrate. One specific technique is the use of sidewall spacers or,simply, spacers. Spacers are typically formed by conformally depositinga spacer material on a mandrel. The mandrel can be a topographic featuresuch as a line, mesa, or hole. Any of various conformal depositionprocesses can be used such as chemical vapor deposition (CVD) or atomiclayer deposition (ALD). The result is a film that covers all surfaces(horizontal and vertical) in a film that has an approximately uniformthickness on both horizontal and vertical surfaces. Next a spacer openetch is executed. A spacer open etch is a directional (anisotropic) etchto remove an amount of spacer material at least equal to the depositedthickness. The result is removing spacer material from horizontalsurface while leaving a spacer on vertical surfaces (sidewalls ofvarious features). The spacer can then be used as a mask or structurefor subsequent microfabrication. Thus, it is important that spacers havethe intended structure for forming features in the substrate having thedesired critical dimension.

SUMMARY

In one embodiment, this disclosure presents a method of patterning asubstrate, the method comprising: forming a patterned photoresiststructure on the substrate, the patterned photoresist structure having asidewall with a predetermined sidewall slope that corresponds to atarget critical dimension (CD) for a substrate feature to be formed inthe substrate; depositing a conformal layer of spacer material on thesidewall; removing the patterned photoresist structure from thesubstrate such that the spacer material remains as a sidewall spacerformed on the substrate; directionally etching the substrate using thesidewall spacer as an etch mask to form the substrate feature having thetarget CD in the substrate.

In one embodiment, the forming a patterned photoresist structurecomprises exposing a layer of photoresist to a pattern of actinicradiation using a mask-based photolithography system, said exposurebeing performed at a defocus point corresponding to the predeterminedsidewall slope.

In one embodiment, the forming a patterned photoresist structurecomprises: forming an underlayer of predetermined material correspondingto forming the predetermined sidewall slope, forming a layer ofphotoresist on the underlayer, exposing the layer of photoresist to apattern of actinic radiation using a mask-based photolithography system,wherein the underlayer enhances the exposing a layer step to form alatent pattern structure corresponding to the patterned photoresiststructure having the predetermined sidewall slope, and removing portionsof the photoresist from the substrate such that the latent patternstructure remains as the patterned photoresist structure on thesubstrate.

In one embodiment, the forming an underlayer comprises forming a layerof material having a predetermined reflectivity configured to, duringthe exposure, increase an intensity of the actinic radiation in a regionof the photoresist that is adjacent to the underlayer such that thelatent pattern structure has the predetermined sidewall slope.

In one embodiment, the forming an underlayer comprises forming a layerof material having reactive species configured to modify a latentpattern structure in a region of the photoresist that is adjacent to theunderlayer such that the latent pattern structure has the predeterminedsidewall slope.

In one embodiment, said predetermined sidewall slope is configured tocompensate for relaxation of stress in the layer of spacer materialafter the removing of the patterned photoresist structure.

In one embodiment, the layer of spacer material on the sidewall forms afirst angle with respect to the substrate surface, and the sidewallspacer forms a second angle with respect to the substrate surface, saidsecond angle being closer to perpendicular than the first angle due therelaxation of stress.

In one embodiment, the target CD is equivalent to a thickness of thelayer of spacer material.

In one embodiment, the forming a patterned photoresist comprises forminganother sidewall in a different region of the substrate which hasanother predetermined sidewall slope that corresponds to another targetcritical dimension (CD), the sidewall slope and another sidewall slopebeing configured to provide uniform CD of substrate features indifferent regions of the substrate.

Another embodiment further comprises forming an underlayer ofpredetermined material corresponding to forming the predeterminedsidewall slope, forming a layer of photoresist on the underlayer,wherein the underlayer enhances the exposing step to form a latentpattern structure corresponding to the patterned photoresist structurehaving the predetermined sidewall slope, and removing portions of thephotoresist from the substrate such that the latent pattern structureremains as the patterned photoresist structure on the substrate.

In one embodiment, this disclosure presents a method of patterning asubstrate, the method comprising: depositing an anti-reflective coatinglayer on a substrate, the anti-reflective coating layer including asolubility-shifting component; depositing a layer of photoresist on theanti-reflective coating layer; exposing the layer of photoresist to apattern of actinic radiation using a mask-based photolithography system,wherein a focus point of the pattern of actinic radiation is set atpredetermined point that creates a latent pattern of structures having asidewall taper in that the upper portions of the structures have widercross-sections as compared to cross-sections of correspondingintermediate portions; diffusing the solubility-shifting component intoa lower portion of the layer of photoresist; and developing the layer ofphotoresist resulting in photoresist structures having the sidewalltaper in that a cross-sectional width of the photoresist structuresdecreases from a top of the photoresist structures to a bottom of thephotoresist structures.

In one embodiment, the layer of photoresist contains a first photo acidgenerator that generates a first photo acid in response to a firstwavelength of light, and wherein the solubility shifting component is asecond photo acid that is a component of a second photo acid generatorthat generates the second photo acid in response to a second wavelengthof light.

In one embodiment, the first wavelength of light is different from thesecond wavelength of light.

Another embodiment further comprises executing a flood exposure on thesubstrate of the second wavelength of light subsequent to exposing thelayer of photoresist to the pattern of actinic radiation using themask-based photolithography system.

In one embodiment, the first wavelength of light is equivalent to thesecond wavelength of light.

In one embodiment, exposure from the pattern of actinic radiation usingthe mask-based photolithography system is sufficient to generate anamount of photo acid from the second photo acid generator.

In one embodiment, the solubility-shifting component is acid depositedon the anti-reflective coating layer.

In one embodiment, the solubility-shifting component is free acid withinthe anti-reflective coating layer.

Another embodiment further comprises forming sidewall spacers on thephotoresist structures, the sidewall spacers adopting the sidewall taperof the photoresist structures; and removing the photoresist structures.

In one embodiment, removing the photoresist structures results in topportions of sidewall spacers from a given photoresist structuredecreasing in geometrical distance from each other as the givenphotoresist structure is removed.

In one embodiment, the anti-reflective coating layer ispartially-reflective and sufficient to reflect a portion of the patternof actinic radiation back into the layer of photoresist to generate morephoto acid at bottom portions of the layer of photoresist.

In one embodiment, a concentration of the solubility-shifting componentin the anti-reflective coating layer is selected so that a sum of photoacid generated from the layer of photoresist and photo acid generatedfrom the anti-reflective coating layer is sufficient to result in thephotoresist structures having the sidewall taper.

In one embodiment, this disclosure presents a method of patterning asubstrate, the method comprising: depositing an anti-reflective coatinglayer on a substrate; depositing a layer of photoresist on theanti-reflective coating layer; exposing the layer of photoresist to apattern of actinic radiation using a mask-based photolithography system,wherein a focus point of the pattern of actinic radiation is set atpredetermined point that creates a latent pattern of structures having asidewall taper in that the upper portions of the structures have widercross-sections as compared to cross-sections of corresponding lowerportions; and developing the layer of photoresist resulting inphotoresist structures having the sidewall taper in that across-sectional width of the photoresist structures decreases from a topof the photoresist structures to a bottom of the photoresist structures.

In one embodiment, this disclosure presents a method of patterning asubstrate, the method comprising: identifying an effective spacer CD toresult from spacers formed on a substrate depositing an anti-reflectivecoating layer on a substrate; depositing a layer of photoresist on theanti-reflective coating layer; exposing the layer of photoresist to apattern of actinic radiation using a mask-based photolithography system,wherein a focus point of the pattern of actinic radiation is set atpredetermined point that creates a latent pattern of structures having apredetermined sidewall taper; developing the layer of photoresistresulting in photoresist structures having the predetermined sidewalltaper; forming sidewall spacers on the photoresist structures, thesidewall spacers adopting the predetermined sidewall taper; and removingthe photoresist structures from the substrate resulting in the sidewallspacers having a modified sidewall taper that creates the effectivespacer CD when transferring a pattern defined by the sidewall spacersinto an underlying layer.

Note that this summary section does not specify every embodiment and/orincrementally novel aspect of the present disclosure or claimedinvention. Instead, this summary only provides a preliminary discussionof different embodiments and corresponding points of novelty overconventional techniques. For additional details and/or possibleperspectives of the invention and embodiments, the reader is directed tothe Detailed Description section and corresponding figures of thepresent disclosure as further discussed below.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a flow chart for one method of patterning a substrate.

FIG. 2 illustrates three different resist profile cases, the resistprofiles after a spacer wrap creating a constant spacer thickness, andthe effective critical dimension versus actual critical dimension foreach of the resist profiles after a spacer etch mandrel pull (SEMP)etch.

FIG. 3 shoes three different resist profiles, where the resist for“−Defocus” has a wider bottom that narrows to the top, the resist for“In Focus” has a top and bottom of approximately equal width, and theresist for “+Defocus” has a wider top that narrows to the bottom.

FIG. 4 shows cross-section transmission electron microscopy (TEM) imagesshowing resist profile tuning by varying focus, where dose=34 mJ/cm².

FIG. 5 illustrates an example of controlling profile via reactivespecies loaded into an underlayer, where the underlayer contains areactive species (e.g. photo acid generator PAG) to generate acid, wherethat acid is then diffused into photoresist, which increases theconcentration of acid in the bottom of the photoresist.

FIG. 6 illustrates resist profile as a function of reactive speciesconcentration loaded into the underlayer, where, for example, as theamount of acid increases in the underlayer, the concentration gradientin the resist becomes steeper.

DETAILED DESCRIPTION

As noted in the Background, it is important that spacers have theintended structure for forming features in the substrate having thedesired critical dimension (CD). Spacers can be formed on mandrels ofany material. Typically a first material formed into a topographicrelief pattern is photoresist. Accordingly, forming spacers onphotoresist patterns is desirable. A significant challenge with usingphotoresist as a mandrel is that photoresist is a relatively softmaterial and is often developed with profiles that do not have verticalprofiles. Sidewalls can be leaning inwardly or outwardly depending onhow a photolithographic exposure is executed. Moreover, when spacers aredeposited on some photoresist or other soft mandrels, compressive ortensile stresses in a deposited film can change a profile of the softmandrels. For example, spacers can be leaning or not perfectly normal tothe substrate surface. Spacers are often used as an etch mask forpattern transfers using a directional etch. Leaning spacers can thencause an effective critical dimension to be much larger than a thicknessof the spacer.

Another challenge with using photoresist mandrels is that sidewallspacers can have a first angle while the photoresist is on thesubstrate, but when the photoresist is removed (exhumed), this removalprocess often results in the sidewall spacers changing an angle relativeto the substrate. So even if initial sidewall spacers were perfectlynormal to the substrate, the mandrel removal process can result insidewall spacers having a different angle, such as leaning more towardeach other.

FIG. 1 is a flowchart walking through a method 100 for one embodiment ofpatterning a substrate.

The first step, S101, is forming a patterned photoresist structure onthe substrate, the patterned photoresist structure having a sidewallwith a predetermined sidewall slope that corresponds to a targetcritical dimension for a substrate feature to be formed in thesubstrate. Then, S102 is depositing a conformal layer of spacer materialon the sidewall. Next, S103 is removing the patterned photoresiststructure from the substrate such that the spacer material remains as asidewall spacer formed on the substrate. Last, S104 is directionallyetching the substrate using the sidewall spacer as an etch mask to formthe substrate feature having the target CD in the substrate. Thepatterned photoresist structure on the substrate can be formed using oneor more of the disclosed techniques, including using retrograde focus,an underlayer to modulate reflectivity, and/or an underlayer loaded witha reactive species to result in a predetermined sidewall taper or slope.

The disclosed techniques provide effective spacer CD control for spacersformed on soft mandrels. That is, disclosed techniques can tune orcorrect different incoming photoresist (i.e. resist) profiles usingvarious methods. FIG. 2 shows a conceptual illustration of resistprofile cases and the resulting effective spacer CD. Cross-sectionalillustrations of 3 different resist profiles on a substrate are shown inthe top/first row (labelled “3 Different Resist Profiles”) of FIG. 2 ,where the photoresist mandrel on the left (labelled “−Defocus”) has awider base and narrows to the top, the photoresist mandrel in the middle(labelled “In Focus”) has a base and top with approximately the samewidth, and the photoresist mandrel on the right (labelled “+Defocus”)has a wider top and narrows to the base. The term “effective spacer CD”is used herein to refer to a projected CD during an RIE (reactive ionetch) transfer. In other words, from a z-direction perspective, aleaning spacer will create a shadow larger than its thickness, and thisshadowed area can become the effective CD. The term “actual CD” is usedherein to refer to a thickness of the spacer. When a spacer has avertical or near vertical orientation, the actual CD is transferredduring an RIE transfer. An example illustration of effective CD vsactual CD is shown in the bottom/third row (labelled “Effective CD vs.Actual CD”) of FIG. 2 .

Because an RIE etch is a directional (anisotropic) etch, a pattern thatis transferred is a shadow of the mask. Thus, a leaning spacer canshadow more than a thickness of a given spacer. A transferred CD canthen appear larger than the actual CD because of shadowing from leaning.This is illustrated in the bottom row of FIG. 2 . Note that an amount ofshadowing or effective CD is depending on an angle of leaning. The firstrow of FIG. 2 shows how an incoming resist profile can have variousdegrees of sidewall angles. In the second/middle row (labelled “ConstantSpacer Thickness”) of FIG. 2 , a deposited spacer from a spacer wrap canfollow the profile of the incoming resist mandrel. Some spacer materialcan also further compress a given photoresist material.

A spacer deposition is a mostly uniform process in which one cannotcontrol the amount of deposition as a function of location on a singlewafer in order to modulate spacer CD. In other words, deposition isuniform across the wafer. Techniques disclosed, however, controleffective spacer CD at specific locations on a wafer for cross-wafercontrol by providing additional knobs to tune the process. A spacer canthen be deposited directly on the photoresist which has a modifiedprofile depending on the desired effective CD. Note that sidewallspacers can have a first angle while the photoresist is on thesubstrate, but when the photoresist is removed (exhumed), this removalprocess often results in the sidewall spacers changing an angle relativeto the substrate. So even if initial sidewall spacers were perfectlynormal to the substrate, the mandrel removal process can result insidewall spacers having a different angle, such as leaning more towardeach other. This can be seen in FIG. 2 . As shown on the left side ofFIG. 2 (“−Defocus” column), when the photoresist mandrel has a widerbase then top, there is an angled sidewall spacer, and after removal,the angle of lean increases. As shown in the middle column of FIG. 2(“In Focus” column), even with perfectly vertical spacers, removal ofthe photoresist mandrel can cause spacer leaning. Accordingly,techniques herein include forming photoresist mandrels with a retrogradeslope or reverse taper; for example, a mandrel with a wider top thatnarrows to base. Initially formed sidewall spacers will then not beperpendicular to the substrate, but after removal of the photoresistmandrel, the removal result in spacers that are normal or perpendicularto the substrate, as can be seen in the right side column of FIG. 2(“+Defocus” column). Thus, in one embodiment, having a reverse taper(i.e. retrograde) profile to result in straight sidewall spacers ispresented. That is, the layer of spacer material on the sidewall mayform a first predetermined angle that is far from perpendicular withrespect to the substrate surface, but designed to compensate forrelaxation of stresses upon removal of the photoresist. Then, afterremoval of the photoresist, the sidewall spacer can form a second anglethat approaches perpendicular (closer to perpendicular than the firstangle) due the relaxation of stress.

One embodiment includes a retrograde focus technique. This includesadjusting focus to modulate a resist profile and side-wall angle (SWA)which impacts the effective spacer CD. Focus offset can be performed ona scanner or a stand-alone platform. FIG. 3 illustrates results of aresist 204 in focus, the resist 202 with focus decreased, and the resist206 with focus increased. A focal point of an exposure pattern isessentially raised to a point higher about the layer of photoresist thenwould normally be used. This is a change of focus in the z-direction.While this positive defocus results in exposing sidewalls at an angle,the change in central point of focus—for some photoresists—can mean theexposure is less likely to cause de-protection reactions at a bottom ofthe layer of photoresist. FIG. 4 is a cross-sectional magnified image ofphotoresist being tuned by adjusting a focus (f) of the exposure. Inthis particular example, the dose was 34 mJ/cm². Note that in the imageon the right (f=−40 nm) of FIG. 4 , upper portions of the lines(mandrels) have a reverse taper, but each line has a footer.Accordingly, techniques herein can also augment exposure to assist withremoval of the footer.

Techniques herein include using a secondary acid (or base) deliver toaugment an initial exposure to remove footers. There are severalalternative embodiments.

In one embodiment, reactive species are loaded into an underlayer (e.g.anti-reflective coating (ARC) layer). One example of a reactive speciesis an acid. Acid within the underlayer diffuses into the resist from theunderlayer, thus increasing acid concentration at the bottom of theexposure region. Extra light is absorbed as opposed to reflecting it(which does not suffer from standing waves) and produces additional aciddiffusing it into the bottom of the resist, aiding in foot mitigation aswell as side wall angle adjustment. Thus, the underlayer can augment orenhance the exposure step to provide a greater concentration of acidthan would be provided without the underlayer, which provides acorresponding greater removal of resist upon development of the resistafter exposure. As another example, the underlayer can include a basethat augments or enhances the exposure step to provide a greaterconcentration of base than would be provided without the underlayer,which provides a corresponding lesser removal of resist upon developmentof the resist after exposure. Further, the underlayer can be made morereflective to some degree, which can increase radiation intensity torelease a greater concentration of acid from the photoresist itself nearthe interface with the underlayer. FIG. 5 is a diagram of a substratesegment illustrating progression of mask-based lithographic exposurewith underlayer loading. FIG. 5 comprises a resist 406 (i.e.photoresist), an underlayer 404, and a substrate 402. In this example,the underlayer 404 (i.e. underlying layer) contains a photo acidgenerator (PAG) to generate acid (e.g. Hf). Alternatively a base couldbe used. The PAG is reactive to actinic radiation 408 from a mask-basedexposure. After generation of the acid, the acid is diffused into theresist 406 with a bake step. This increases a concentration of acid inbottom portions of the resist 406. Note that the layer of photoresist406 includes photo-reactive species, such as a PAG, but activation atlower portions of the layer of photoresist 406 can be less thanactivation at upper portions of the layer of photoresist 406. Thus,having a second supply of acid that can be brought into the layer ofphotoresist 406 from the underlayer can assist with uniformprotection/deprotection (solubility changing) to be able to increaseresolution or sidewall angle during development.

FIG. 6 illustrates how the use of reactive species loading into theunderlayer 404 can be used as foot mitigation as well. Profile is afunction of reactive species concentration loaded into the underlayer404. For this example, as the amount of acid increases in the underlayer404, the concentration gradient in the resist becomes steeper, as shownby the different shapes of photoresist 406.

In embodiments with two different PAGs (one in the photoresist and onein the ARC layer), they can be responsive to the same wavelength oflight or different wavelengths of light (out-of-band illumination). Forexample, after an initial patterned exposure using a 193 nm wavelengthscanner, an I-line flood exposure can be executed to activate an amountof PAG in the ARC. Note that with a flood exposure, photo acid will begenerated uniformly, but the amount generated can be insufficient byitself to dissolve the layer of photoresist, but when combined withanother acid, the sum is sufficient for dissolution. For example, thetrenches can receive a certain amount of acid, and the under layer canprovide a remaining amount of acid to remove footers and yield thereverse taper profile. In another embodiment, more than two PAGs may beused to achieve the desired results.

In another embodiment, underlayer reflectivity is modulated. An amountof reflectivity of a given underlayer is adjusted by changing a materialcomposition. By reflecting more light from the underlayer, an acidconcentration near the underlayer increases and affects the resistprofile. In other embodiments, a thickness of the anti-reflectivecoating can be adjusted for desired acid concentration and/orreflectivity.

Accordingly, in one example embodiment, a side-wall angle adjustment canadjust the effective CD by sub-nanometer to nanometer corrections.

In the preceding description, specific details have been set forth, suchas a particular geometry of a processing system and descriptions ofvarious components and processes used therein. It should be understood,however, that techniques herein may be practiced in other embodimentsthat depart from these specific details, and that such details are forpurposes of explanation and not limitation. Embodiments disclosed hereinhave been described with reference to the accompanying drawings.Similarly, for purposes of explanation, specific numbers, materials, andconfigurations have been set forth in order to provide a thoroughunderstanding. Nevertheless, embodiments may be practiced without suchspecific details. Components having substantially the same functionalconstructions are denoted by like reference characters, and thus anyredundant descriptions may be omitted.

Various techniques have been described as multiple discrete operationsto assist in understanding the various embodiments. The order ofdescription should not be construed as to imply that these operationsare necessarily order dependent. Indeed, these operations need not beperformed in the order of presentation. Operations described may beperformed in a different order than the described embodiment. Variousadditional operations may be performed and/or described operations maybe omitted in additional embodiments.

“Substrate” or “target substrate” as used herein generically refers toan object being processed in accordance with the invention. Thesubstrate may include any material portion or structure of a device,particularly a semiconductor or other electronics device, and may, forexample, be a base substrate structure, such as a semiconductor wafer,reticle, or a layer on or overlying a base substrate structure such as athin film. Thus, substrate is not limited to any particular basestructure, underlying layer or overlying layer, patterned orun-patterned, but rather, is contemplated to include any such layer orbase structure, and any combination of layers and/or base structures.The description may reference particular types of substrates, but thisis for illustrative purposes only.

Those skilled in the art will also understand that there can be manyvariations made to the operations of the techniques explained abovewhile still achieving the same objectives of the invention. Suchvariations are intended to be covered by the scope of this disclosure.As such, the foregoing descriptions of embodiments of the invention arenot intended to be limiting. Rather, any limitations to embodiments ofthe invention are presented in the following claims.

1. A method of patterning a substrate, the method comprising: depositingan anti-reflective coating layer on a substrate, the anti-reflectivecoating layer including a solubility-shifting component; depositing alayer of photoresist on the anti-reflective coating layer; exposing thelayer of photoresist to a pattern of actinic radiation using amask-based photolithography system, wherein a focus point of the patternof actinic radiation is set at predetermined point that creates a latentpattern of structures having a sidewall taper in that the upper portionsof the structures have wider cross-sections as compared tocross-sections of corresponding intermediate portions; diffusing thesolubility-shifting component into a lower portion of the layer ofphotoresist; and developing the layer of photoresist resulting inphotoresist structures having the sidewall taper in that across-sectional width of the photoresist structures decreases from a topof the photoresist structures to a bottom of the photoresist structures.2. The method of claim 1, wherein the layer of photoresist contains afirst photo acid generator that generates a first photo acid in responseto a first wavelength of light, and wherein the solubility-shiftingcomponent is a second photo acid that is a component of a second photoacid generator that generates the second photo acid in response to asecond wavelength of light.
 3. The method of claim 2, wherein the firstwavelength of light is different from the second wavelength of light. 4.The method of claim 3, further comprising executing a flood exposure onthe substrate of the second wavelength of light subsequent to exposingthe layer of photoresist to the pattern of actinic radiation using themask-based photolithography system.
 5. The method of claim 1, whereinthe solubility-shifting component is acid deposited on theanti-reflective coating layer.
 6. The method of claim 1, wherein thesolubility-shifting component is free acid within the anti-reflectivecoating layer.
 7. The method of claim 1, further comprising: formingsidewall spacers on the photoresist structures, the sidewall spacersadopting the sidewall taper of the photoresist structures; and removingthe photoresist structures.
 8. The method of claim 7, wherein removingthe photoresist structures results in top portions of sidewall spacersfrom a given photoresist structure decreasing in geometrical distancefrom each other as the given photoresist structure is removed.
 9. Themethod of claim 1, wherein the anti-reflective coating layer ispartially-reflective and sufficient to reflect a portion of the patternof actinic radiation back into the layer of photoresist to generate morephoto acid at bottom portions of the layer of photoresist.
 10. Themethod of claim 1, wherein a concentration of the solubility-shiftingcomponent in the anti-reflective coating layer is selected so that a sumof photo acid generated from the layer of photoresist and photo acidgenerated from the anti-reflective coating layer is sufficient to resultin the photoresist structures having the sidewall taper.